Organic electroluminescent element

ABSTRACT

Disclosed is the use of a novel coumarin derivative with a specific molecular structure. The physical and optical properties of said coumarin derivative render it very useful as a luminescence-assisting agent to be used in highly durable organic EL devices.

TECHNICAL FIELD

This invention relates to an organic electroluminescent device(abbreviated as “organic EL device” hereinafter), more particularly, toan organic EL device using a novel coumarin derivative.

BACKGROUND ART

In the field of information display, organic EL devices have beenhighlighted as displaying devices of the forthcoming generation.Hitherto, cathode-ray tubes have been predominantly used in informationdisplaying equipments of larger sizes such as computer termini and TVreceivers: However, cathode-ray tubes are large in volume and weight andhigh in operation voltage, and these may restrict their application inequipments which are directed to use at home, as well as in compactequipments where portability is one of important factors. More requiredare information displaying equipments which are in a thinner and lighterpanel form and operable with a lower voltage and less power consumption.Liquid crystal devices have been frequently used in various fieldsbecause of the merit that they are operable with a low voltage and lesspower consumption. Liquid crystal devices however have the demerits thatone hardly receives a clear information therefrom when he or she viewsthem at an angle outside the specific ranges, as well as that theirpower consumption is not so small as expected because they usuallyrequire backlight. Organic EL device has appeared as informationdisplaying means which may overcome these demerits.

Organic EL device is a class of light-emitting device which utilizeselectroluminescence such as fluorescence or phosphorescence: It usuallycomprises a luminescent layer incorporated with a luminescent compoundand inserted between a cathode and anode to which dc voltage isenergized to inject holes and electrons in the luminescent layer so thata pair of hole and electron recouple each other to make in theluminescent compound an excited state which subsequently returns to theground state to emit such luminescence. Organic EL device ischaracterized in that its luminescent color tint can be controlled to adesired level by selecting an appropriate organic compound to be used ashost compound in the formation of luminescent layer, and screening guestcompounds (or dopants) which may match with the host compound. This mayremarkably increase the brightness and life expectancy for luminescencein organic EL device, dependently upon the combination of host and guestcompounds. Organic EL device has been deemed to be in principle anexcellent device because of the merit that it does realize an autonomouslight emission and this would advantageously save power consumption.

Many of organic EL devices proposed hitherto however have thedisadvantage that they are low in durability, and therefor theirbrightness decreases within a short period of time when used undersevere conditions, for example, in case of equipping them to automobileswhere mechanical vibrations and high temperatures are unavoidable.

In view of such situation, the objectives of this invention are toprovide a luminescence-assisting agent which would be useful even inhighly durable organic EL devices, as well as to provide its uses.

DISCLOSURE OF INVENTION

To attain these objectives, the present inventors eagerly researched andscreened coumarin derivatives, resulting in the finding that in organicEL devices, a coumarin derivative which comprises a coumarin ring, anaphthalene ring with one or more hydrocarbon groups, and afive-membered heterocycle condensed with the naphthalene ring so as togive an electronic resonance through the coumarin and naphthalene ringsgives no luminescence, but effectively accelerates the transfer ofexcited energy in host compound to guest compound when used incombination with appropriate host and guest compounds: As the result, ahighly bright electroluminescence consistently prolongs over a longperiod of time even under severe conditions.

Particularly, this invention attains the above objective by providing anorganic EL device which uses as a luminescence-assisting agent thecoumarin derivative represented by either General Formula 1 or 2:

(In General Formulae 1 and 2, X denotes carbon atom or a heteroatom. R¹to R¹⁴ independently denote hydrogen atom or an arbitrary substituent,provided that R³ and/or R⁴ are apparently absent when R¹ and/or R² forma ring structure containing both the nitrogen atom linked with R¹ and/orR² and the carbon atom linked with R³ or R4. At least one of R⁹ to R¹⁴is a hydrocarbon group which may bear a substituent. In case that X is adivalent or trivalent heteroatom, R⁷ and/or R⁸ are absent.)

This invention also attains the above objective by providing a displaypanel which uses such organic EL device.

In addition, this invention attains the above objective by providing aninformation displaying equipment which uses such organic EL device.

Furthermore, this invention attains the above objective by providing aluminescence-assisting agent for use in organic EL device which employsthe coumarin derivative represented by either General Formula 1 or 2:

(In General Formulae 1 and 2, X denotes carbon atom or a heteroatom. R¹to R¹⁴ independently denote hydrogen atom or an arbitrary substituent,provided that R³ and/or R⁴ are apparently absent when R¹ and/or R² forma ring structure containing both the nitrogen atom linked RI and/or R²and the carbon atom linked with R³ or R⁴. At least one of R⁹ to R¹⁴ is ahydrocarbon group which may bear a substituent. In case that X is adivalent or trivalent heteroatom, R⁷ and/or R⁸ are absent.)

Either of the coumarin derivatives represented by General Formula 1 or 2is a novel organic compound which has not been documented inliteratures. This invention is based on the creation of novel organiccompounds, as well as on the discovery of their properties useful inindustries.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a brief figure of an example for organic EL device accordingto this invention.

FIG. 2 is a brief figure of an example for display panel according tothis invention.

FIG. 3 is a block diagram of an example for information displayingequipment according to this invention.

In the Figures, the reference numerals 1 and 10 represent substrates; 2and 14, anodes; 3 and 16, hole transportation layers; 4 and 18,luminescent layers; 5, an electron transportation layer; 6 and 20,cathodes; 30, a dc source; 32 and 34, voltage-elevating circuits; 36 and46, driving circuits; 38, a microcomputer; 40, a clock pulse-generatingcircuit; 42 and 44, oscillating circuits; and 48, a display panel.

BEST MODE FOR CARRYING OUT THE INVENTION

The following is to explain embodiments according to this invention: Asmentioned heretofore, this invention relates to an organic EL deviceusing as luminescence-assisting agent the coumarin derivativerepresented by either General Formula 1 or 2. The wording“luminescence-assisting agent” as reffered to in this invention means aluminescent organic material to be used together with host and guestcompounds to form a luminescent layer in an organic EL device, whichnever gives a luminescence and only accelerates the transfer of excitedenergy in host compound to guest compound to assist the luminescence ofother compounds.

In General Formulae 1 and 2, X denotes carbon atom or a heteroatom. Asto the heteroatom in X, usually, one can choose an atom of the group 15or 16 in the periodic chart of elements, such as nitrogen, oxygen,sulfur, selenium and tellurium atoms. Among these carbon andheteroatoms, carbon, nitrogen, oxygen and sulfur atoms are preferablebecause coumarin derivatives with such atom are superior in opticalproperties and producibilities.

R¹ to R¹⁴ in General Formulae 1 and 2 independently denote hydrogen atomor an arbitrary substituent. The substituents in R¹ to R¹⁴ are, forexample, aliphatic hydrocarbon groups with a carbon number of up to 20,such as methyl, ethyl, propyl, isopropyl, isopropenyl, 1-propenyl,2-propenyl, butyl, isobutyl, sec-butyl, tert-butyl, 2-butenyl,1,3-butadienyl, pentyl, isopentyl, neopentyl, tert-pentyl,1-methylpentyl, 2-methylpentyl, 2-pentenyl, hexyl, isohexyl,5-methylhexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl andoctadecyl groups; alicyclic hydrocarbon groups such as cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl, cyclohexenyl and cycloheptylgroups; aromatic hydrocarbon groups such as phenyl, o-tolyl, m-tolyl,p-tolyl, xylyl, mesityl, o-cumenyl, m-cumenyl, p-cumenyl, benzyl,phenethyl and biphenylyl groups; ether groups such as methoxy, ethoxy,propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy,pentyloxy, phenoxy and benzyloxy groups; ester groups such asethoxycarbonyl, propoxycarbonyl, acetoxy and benzoyloxy groups; halogengroups such as fluoro, chloro, bromo and iodo groups; hydroxy group;carboxy group; cyano group; nitro group; and combinations thereof.

Dependently upon uses, it is preferable to choose as substituents in R¹and R² an aliphatic, alicyclic, aromatic hydrocarbon or combinationthereof, while those in R⁶, for example, short-chain aliphatichydrocarbon groups such as methyl, ethyl, propyl, isopropyl, butyl,isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl andtert-pentyl groups; ether groups such as methoxy, ethoxy, propoxy,isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentyloxy,phenoxy and benzyloxy groups; ester groups such as methoxycarbonyl,ethoxycarbonyl, propoxycarbonyl, acetoxy and benzoyloxy groups; andcyano group: One or more hydrogen atoms in these substituents may bereplaced by halogen group(s) such as fluoro group. As mentionedheretofore, at least one of the substituents in R⁹ to R¹⁴ is ahydrocarbon group such as aliphatic, alicyclic or aromatic hydrocarbongroup or a combination thereof: Among these, it is preferable to choosean aliphatic hydrocarbon group, in particular, an aliphatic hydrocarbongroup having a branched-chain structure and a carbon number of up to 6,such as isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl,neopentyl, tert-pentyl, 1-methylpentyl, 2-methylpentyl and isohexylgroups. As to the substituents in R⁷ and R⁸, it is preferable to choosea similar aliphatic, alicyclic or aromatic hydrocarbon group or acombination thereof as those in R¹ and R², provided that X is a divalentor trivalent heteroatom, and R⁷ and/or R⁸ are absent. In case that thecarbon linked with R³ and/or R⁴ forms no ring structure such aspiperidine or julolidine ring, one can choose as R³ and/or R⁴ hydrogenatom or an arbitrary substituent as described above, dependently uponuses. As to R⁵, one can choose hydrogen atom or hydroxyl group becausecoumarin derivatives therewith are superior in producibility, andalternatively an ether or ester group as described above whileconsidering the uses of coumarin derivatives.

In certain applications such as organic EL device whereluminescence-releasing ability is one of important factors, it ispreferable to choose a coumarin derivative as represented by GeneralFormula 3 or 4, where both R¹ and R² are aliphatic hydrocarbon groupswhich are in the linkage with the carbon atom bound to either R³ or R⁴forming julolidine ring. In General Formulae 3 and 4, X denotes carbonor a heteroatom similar to that in General Formula 1 or 2, while R⁵ toR¹⁴ denote hydrogen or an arbitrary substituent similar to those inGeneral Formula 1 or 2 and at least one of R⁹ to R¹⁴, a hydrocarbongroup. R¹⁵ to R¹⁸ independently denote hydrogen or an aliphatichydrocarbon group: Among these, it is preferable to choose as aliphatichydrocarbon group a short-chain aliphatic hydrocarbon group such asmethyl, ethyl, propyl, butyl or pentyl group. Among the coumarinderivatives represented by General Formula 3 or 4, those where at leastone of R⁹ to R¹⁴ is a branched aliphatic hydrocarbon group such asisopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl,tert-pentyl, 1-methylpentyl, 2-methylpentyl or isohexyl group arecharacterized in that they are superior in luminescence-assistingability and solubility in usual organic solvents, as well as in thattheir luminescence-assisting abilities are hardly weakened even underconditions where elevated temperatures are unavoidable because they arehigh in glass transition point and therefore large in thermal stability.

The coumarin derivatives represented by Chemical Formulae 1 to 27 areillustrative for those feasible in this invention. These effectivelyaccelerate the transfer of excited energy in host compound to guestcompound when used as luminescence-assisting agent in organic ELdevices. Many of the coumarin derivatives represented by General Formula1 or 2 are significantly higher in glass transition point (130° C. orhigher), in particular, 150° C. or higher dependently upon substituentsas seen in the coumarin derivative represented by Chemical Formula 18,and, as the result, larger in thermal stability in comparison withconventional analogous compounds. The glass transition point of thecoumarin derivative according to this invention can be determined, forexample, by usual differential scanning calorimetry (abbreviated as “DSCanalysis” hereinafter) as described later.

The coumarin derivatives feasible in this invention can be prepared byvarious ways: With an economical viewpoint, it is preferable to employ aprocess including the step of allowing the compound represented byGeneral Formula 7 which has R¹ to R⁶ corresponding to those in GeneralFormula 1 or 2 to react with the compound represented by General Formula8 or 9 which has R⁷ to R¹⁴ corresponding to those in General Formula 1or 2. In General Formula 8 or 9, in case that X is a divalent ortrivalent heteroatom, H¹ and H² are absent.

Particularly, adequate (usually roughly equimolar) amounts of thecompound represented by General Formula 7 and the compound representedby General Formula 8 or 9 are placed in a reaction vessel, dissolved inan appropriate solvent, if necessary, admixed with either a basiccompound, for example, sodium hydroxide, potassium hydroxide, sodiumcarbonate, potassium carbonate, sodium hydrogencarbonate, sodiumacetate, ammonia, triethylamine, piperidine, pyridine, pyrrolidine,aniline, N,N-dimethylaniline or N,N-diethylaniline, an acidic compoundsuch as hydrochloric acid, sulfuric acid, nitric acid, acetic acid,acetic anhydride, trifluoroacetic acid, p-toluenesulfonic acid,methanesulfonic acid or trifluromethanesufonic acid or a Lewis acidiccompound such as aluminium chloride, zinc chloride, tin tetrachloride ortitanium tetrachloride, and then allowed to react at ambient or highertemperature while stirring under refluxing conditions.

As to solvents, one can choose hydrocarbons such as pentane, hexane,cyclohexane, octane, benzene, toluene and xylene; halides such as carbontetrachloride, chloroform, 1,2-dichloroetane, 1,2-dibromoethane,trichloroetylene, tetrachloroethylene, chlorobenzene, bromobenzene andα-dichlorobenzene; alcohols and phenols such as methanol, ethanol,1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol,isopentyl alcohol, cyclohexanol, ethylene glycol, propylene glycol,2-methoxyethanol, phenol, benzyl alcohol, cresole, diethylene glycol,triethylene glycol and glycerin; ethers such as diethyl ether,diisopropyl ether, tetrahydrofuran, tetrahydropyran, 1,4-dioxane,anisole, 1,2-dimethoxyethane, diethylene glycol dimethyl ether,dicyclohexyl-18-crown-6, methylcarbitol and ethylcarbitol; acids andacid derivatives such as acetic acid, acetic anhydride, trichloroaceticacid, trifluoroacetic acid, propionic anhydride, ethyl acetate, butylcarbonate, ethylene carbonate, propylene carbonate, formamide,N-methylformamide, N,N-dimethylformamide, N,N-dimethylacetoamide,hexamethylphosphoric triamide and phosphoric trimethyl; nitriles such asacetonitrile, propionitrile, succinonitrile and benzonitrile; nitrocompounds such as nitromethane and nitrobenzene; sulfur-containingcompounds such as dimethylsulfoxide and sufolane; and water which may beused in combination, if necessary.

In case of using solvents, generally, a larger amount of solvent leadsto a less reaction efficiency, while a less amount of solvent, a moredifficulty in homogenous heating and stirring and also in a moreliability of side reactions. Thus, it is desirable to set the amount ofsolvent to a level of up to 100-folds, usually, 5 to 50-folds by weightagainst the total amounts of material compounds to be used. The reactioncompletes within 10 hours , usually, 0.5 to 5 hours, dependently uponthe type of material compounds and reaction conditions. The progress ofreaction can be monitored by conventional method, for example, thinlayer chromatography, gas chromatography and high-performance liquidchromatography. The coumarin derivatives feasible in this invention areobtainable in a good yield by or in accordance with such process. Thecompounds represented by General Formulae 7 to 9 are obtainable by usualmethods which are to prepare analogous compounds.

Prior to uses, the coumarin derivatives thus obtained are usuallypurified with a method(s) usually employed in the purification ofanalogous compounds, such as dissolution, extraction, separation,decantation, filtration, concentration, thin layer chromatography,column chromatography, gas chromatography, high-performance liquidchromatography, distillation, sublimation and crystallization which maybe applied in combination, if necessary. Dependently upon the type ofcoumarin derivatives and uses of organic EL devices, it is desirable tohighly purify coumarin derivatives with distillation, crystallizationand/or sublimation, prior to their uses.

Among these, sublimation is superior to others because high-puritycrystals can be easily obtained through a single step with a less lossfor coumarin derivatives during purification, as well as because solventis not incorporated in crystals. Although both atmospheric and reducedpressure sublimation methods are applicable to this invention, thelatter method is usually employed. To sublimate coumarin derivatives invacuo, for example, an adequate amount of a coumarin derivative isplaced in a sublimation purification apparatus, and then heated at thelowest possible temperature, in particular, at a temperature lower thanits melting point while keeping the pressure inside the apparatus at10⁻² Torr or lower, desirably, 10⁻³ Torr or lower so that the coumarinderivative does not cause decomposition. When the purity of a coumarinderivative to be subjected to sublimation purification is lower, thesublimation rate is reduced so as to avoid the incorporation ofimpurities by increasing or decreasing the pressure and/or heatingtemperature in the apparatus, while the sublimation is accelerated byaerating the inner space of the apparatus with an inert gas such as raregas when a coumarin derivative is less sublimatable. The size ofcrystals obtained by sublimation can be controlled by elevating orreducing temperature at the condensation surface in the apparatus: Whenthe condensation surface is kept at a temperature slightly lower thanheating temperature so that the coumarin derivative graduallycrystallizes, one can obtain crystals of a larger size.

As described heretofore, the coumarin derivative according to thisinvention is very useful as luminescence-assisting agent in organic ELdevices because when used in combination with appropriate host and guestcompounds, it effectively accelerates the transfer of excited energy inhost compound to guest compound, as well as exhibiting a large thermalresistance and giving a stable thin membrane in glass state. The wording“organic EL device(s)” as referred to as in this invention meanselectroluminescent devices in general which use such coumarin derivativeas luminescence-assisting agent: One of the most important targets towhich this invention is applied is an organic EL device of mono- ormulti-layer type comprising a cathode to be energized with a positivevoltage, an anode to be energized with a negative voltage, a luminescentlayer where hole and electron are allowed to recouple each other so asto obtain a luminescence, and arbitrarily a holeinjection/transportation layer for injecting and transporting holes fromthe cathode, an electron injection/transportation layer for injectingand transporting electrons from the anode, and a hole-blocking layer forsuppressing the transportation of holes from the luminescent layer tothe electron injection/transportation layer.

As well known in the art, the action mechanism of organic EL devicesessentially consists of the steps of injecting electrons and holes fromelectrodes, allowing the electrons and holes to move in solids, allowingthe electrons and holes to recouple to give singlet or triplet excitons,and allowing the excitons to emit a luminescence: Mono- andmulti-layered organic EL devices are essentially indifferent each otherin these steps. However, in mono-layered organic EL devices, thecharacteristics of the above four steps can not be improved if onechanges the molecular structure of luminescent compounds, while inmulti-layered organic EL devices, the properties required in each stepcan be distributed to a plurality of materials which are independentlyoptimized: Thus, multi-layered organic EL devices attain a prescribedperformance more easily than mono-layered organic EL devices.

Because of these, the organic EL device of this invention will beexplained hereinafter with reference to an example for multi-layeredorganic EL device. FIG. 1 is a brief figure of an example formulti-layered organic EL device according to this invention. In FIG. 1,the reference numeral 1 represents a substrate which is provided byforming a substrate material including a glass such as aluminosilicateglass, aluminoborosilicate glass, silica glass, soda lime glass, bariumsilicate glass, barium borosilicate glass or borosilicate glass; aplastic such as aramid, acrylic resin, polyallylate, polyimide,polyurethane, polyetherketone, polyethersulfon, polyester, polyethylene,poly (ethylene terephthalate), polyolefin, polycarbonate, polysulfon,poly (vinyl chloride), polypropylene, poly (methyl acrylate), epoxyresin, phenol resin, fluorine resin or melamine resin; or a ceramic suchas alumina, silicon, silica or silicon carbide into a plate, sheet orfilm which may be laminated each other, if necessary. Preferredsubstrate materials are a glass for photomask such as aluminosilicateglass, aluminoborosilicate glass, silica glass, borosilicate glass andbarium borosilicate glass which are low in both alkali content andthermal expansion coefficient, plane and free of scratch on theirsurface and easily grindable; and plastics such as aramids, epoxys,phenols, polyallylates, polyimides, polyesters, aromatic polyethers,polyolefins, melamines and fluorines which are superior in affinity toadjacent electric conductive membrane and less in moisture permeability,while opaque ceramic materials such as silicon may be used incombination with transparent electrode material(s). When it is necessaryto control the chromaticity of luminescence, chromaticity adjustingmeans such as filter membrane, chromaticity conversion membrane anddielectric reflection membrane is provided in an appropriate part of thesubstrate 1.

The reference numeral 2 represents an anode, which is formed bypreparing one or more metals or electric conductive compounds low inelectric resistivity but high in optical transmissivity throughout thevisible region into a single or plurality of membrane(s) with athickness of 10 to 1,000 nm, desirably, 50 to 500 nm to give an electricresistivity of 1 kΩ/□ or lower, desirably, 5 to 50 Ω/□ for the anode 2with a method such as vacuum deposition, spattering, chemical vapordeposition (CVD), atom layer epitaxy (ALE), embrocation or immersionwhile allowing the membrane(s) to contact with either surface of thesubstrate 1. Examples of electric conductive materials feasible in theanode 2 are metals such as gold, platinum, aluminium and nickel; metaloxides such as zinc oxide, tin oxide, indium oxide and mixtures of tinoxide and indium oxide (abbreviated as “ITO” hereinafter); and electricconductive oligomers and polymers of repeating aniline, thiophene orpyrrole units. Among these, ITO is characterized in that one can easilyobtain preparations with a reduced resistivity, as well as in thatminute patterns can be easily provided by etching with acids.

The reference numeral 3 represents a hole injection/transportationlayer, which is usually formed with a method similar to that in theanode 2 by preparing the hole injection/transportation layer materialinto a membrane with a thickness of 1 to 1,000 nm while allowing it tocontact with the anode 2. As to hole injection/transportation layermaterials, it is desirable to choose a material which exhibits a lowionization potential and a hole mobility of, for example, at least10^(−6 cm) ²/V• second under an electric field of 10⁴ to 10⁶ V/cm so asto facilitate the injection and transportation of holes from the anode2. Particular hole injection/transportation layer materials are, forexample, arylamine, imidazole, oxadiazole, oxazole, triazole, chalcone,styryl anthracene, stilbene, tetraarylethene, triarylamine,triarylethene, triarylmethane, phthalocyanine, fluorenone, hydrazone,N-vinylcarbazole, pyrazoline, pyrazolone, phenylanthracene,phenylenediamine, polyarylalkane, polysilane, polyphenylenevinylene andporphyrin derivatives which are usually used in organic EL devices:These may be used in combination, if necessary. Among these, the muchmore preferable are monomers and polymers in an aromatic tertial amineform which are of an arylamine such as monoarylamine, diarylamine,triarylamine and tetraarylamine.

The reference numeral 4 represents a luminescent layer, which is usuallyformed with a method similar to those in the anode 2 by preparing one ormore coumarin derivatives of this invention with or without premixing anappropriate host and guest compounds into a single or adjacent separatemembrane(s) with a thickness of 1 to 1,000 nm, preferably, 2 to 200 nmwhile allowing it or them to contact with the holeinjection/transportation layer 3. Dependently upon the types of host andguest compounds to be used in combination, the ratio of the guestcompound(s) against the host compound(s) is usually in the range of 0.1to 10 mol % , desirably, 0.5 to 5 mol % while the coumarin derivative ofthis invention as luminescence-assisting agent is usually used in therange of 0.1:10 to 10:0.1, desirably, 0.5:5 to 5:0.5 against guestcompound in terms of the molar ratio. The luminescence-assisting agentfor use in organic EL device according to this invention never hinderthe incorporation of luminescent organic compound(s) other than thoserepresented by General Formula 1 or 2: One or more otherluminescence-assisting agents can be arbitrarily incorporated thereto,if necessary, as long as such incorporation does not fall outside theobjectives of this invention. For example, the coumarin compoundsdisclosed in Japanese Patent Kokai No. 2001-76876 are illustrative forsuch auxiliary luminescence-assisting agent.

Particular host compounds to be used in combination with theluminescence-assisting agent of this invention are, for example,quinolinol metal complexes, condensed polycyclic aromatic hydrocarbons,for example, anthracene, chrysene, coronene, triphenylene, naphthacene,naphthalene, phenantlene, picene, pyrene, fluolene, perylene,benzopylene and their derivatives; hydrocarbon ring assemblies such asquaterphenyl, 1,4-diphenylbutadiene, terphenyl, stilbene,tetraphenylbutadiene, biphenyl and their derivatives; heterocycliccompounds such as oxadiazole, carbazole, pyridazine, benzimidazole,benzoxazole, benzothiazole and their derivatives; quinacridone, rubrenecompounds and their derivatives; and polymethyne dyes of stylyl typewhich are usually used in organic EL devices.

Among these, it is preferable to choose quinolinol metal complexes,copper phthalocyanines and aromatic tertiary amines such as N⁴,N⁴′-dinaphthalene-1-yl-N⁴, N⁴′-diphenyl-biphenyl-4, 4′-diamine, N⁴,N⁴′-diphenyl-N⁴, N⁴′-di-m-tolyl-biphenyl-4,4′-diamine, N⁴, N⁴, N⁴′,N⁴′-tetrakis-biphenyl-4-yl-biphenyl-4, 4′-diamine andtris-[4-(phenyl-m-tolyl-methyl)-phenyl]-amine with respect to energytransferring efficiency. The wording “quinolinol metal complex(es)” asreferred to as in this invention means complexes in general comprising aquinolinol, such as 8-quinolinol and benzoquinoline-10-ol, which bearsin the same molecule a pyridine residue and hydroxyl group and behavesas ligand; and a univalent, divalent or trivalent metal or its oxide ofthe group 1, 2, 12 or 13 in the periodic chart of elements, such aslithium, sodium, potassium, beryllium, magnesium, calcium, zinc, boron,aluminium, galium and indium, which behaves as center metal and receivesan electron pair from the nitrogen atom in the pyridine residue to forma coordinate bond with the ligand. In case that ligand is either8-quinolinol or benzoquinoline-10-ol, it may bear one or moresubstituents, never hindering one or more substituents, for example,halogen groups such as fluoro, chloro, bromo and iodo groups; aliphatichydrocarbon groups such as methyl, trifluoromethyl, ethyl, propyl,isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl,neopentyl and tert-pentyl groups; ether groups such as methoxy,trifluoromethoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy,sec-butoxy, tert-butoxy, pentyloxy, isopentyloxy, hexyloxy, phenoxy andbenzyloxy groups; ester groups such as acetoxy, trifluoroacetoxy,benzoylacetoxy, methoxycalbonyl, trifluoromethoxycalbonyl,ethoxycalbonyl and propoxycalbonyl groups; cyano group; nitro group andsulfone group to be bound to carbon(s) other than those at the 8- or10-positions to which hydoxyl group(s) is linked. In case that aquinolinol metal complex has two or more ligands in the same molecule,they may be the same or different each other.

Particular quinolinol metal complexes are, for example, aluminiumcomplexes such as aluminium-tris(8-quinolinolato),aluminium-tris(3,4-dimethyl-8-quinolinolato),aluminium-tris(4-methyl-8-quinolinolato),aluminium-tris(4-methoxy-8-quinolinolato),aluminium-tris(4,5-dimethyl-8-quinolinolato),aluminium-tris(4,6-dimethyl-8-quinolinolato),aluminium-tris(5-chloro-8-quinolinolato), aluminium-tris(5-bromo-8-quinolinolato), aluminium-tris(5,7-dichloro-8-quinolinolato),aluminium-tris(5-cyano-8-quinolinolato),aluminium-tris(5-sulfonyl-8-quinolinolato),aluminium-tris(5-propyl-8-quinolinolato) andaluminium-tris(2-methyl-8-quinolinolato); zinc complexes such aszinc-bis(8-quinolinolato), zinc-bis(2-methyl-8-quinolinolato),zinc-bis(2,4-dimethyl-8-quinolinolato),zinc-bis(2-methyl-5-chloro-8-quinolinolato), zinc-bis(2-methyl-5-cyano-8-quinolinolato),zinc-bis(3,4-dimethyl-8-quinolinolato),zinc-bis(4,6-dimethyl-8-quinolinolato),zinc-bis(5-chloro-8-quinolinolato) andzinc-bis(5,7-dichloro-8-quinolinolato); beryllium complexes such asberyllium-bis(8-quinolinolato), beryllium-bis(2-methyl-8-quinolinolato),beryllium-bis(2,4-dimethyl-8-quinolinolato), beryllium-bis(2-methyl-5-chloro -8-quinolinolato),beryllium-bis(2-methyl-5-cyano-8-quinolinolato), beryllium-bis(3,4-dimethyl-8-quinolinolato),beryllium-bis(4,6-dimethyl-8-quinolinolato),beryllium-bis(5-chloro-8-quinolinolato),beryllium-bis(4,6-dimethyl-8-quindlinolato) andberyllium-bis(10-hydroxybenzo[h]quinolinolato); magnesium complexes suchas magnesium-bis(8-quinolinolato),magnesium-bis(2-methyl-8-quinolinolato),magnesium-bis(2,4-dimethyl-8-quinolinolato),magnesium-bis(2-methyl-5-chloro-8-quinolinolate),magnesium-bis(2-methyl-5-cyano-8-quinolinolato),magnesium-bis(3,4-dimethyl-8-quinolinolato),magnesium-bis(4,6-dimethyl-8-quinolinolato),magnesium-bis(5-chloro-8-quinolinolato) andmagnesium-bis(5,7-dichloro-8-quinolinolato); indium complexes such asindium-tris(8-quinolinolato); gallium complexes such asgallium-tris(5-chloro-8-quinolinolato); and calcium complexes such ascalcium-bis(5-chloro-8-quinolinolato) which may be used in combination,if necessary. The above host compounds are listed only for illustration,and intended in no way to limit to these the host compounds feasible inthis invention.

Examples of guest compounds to be used in combination with theluminescence-assisting agent according to this invention arequinuclidone, coumarin, thiopyran, pyran, perylene, rubrene and theirderivatives which are usually used in this art: These may be used incombination, if necessary. These are listed only for illustration, andintended in no way to limit to these the guest compounds to be used incombination with the luminescence-assisting agent according to thisinvention. Among these, pyran compounds such as dicyanomethylenepyran,dicyanomethylenethiopyran and coumarin compounds are preferred withrespect to energy transferring efficiency. For example, General Formula5 is illustrative for such dicyanomethylenepyran anddicyanomethylenethiopyran compounds.

In General Formula 5, Y denotes a heteroatom selected from oxygen andsulfur atoms. R¹⁹ denotes an aminostyryl group, while R²⁰ denotes eitheranother aminostyryl group or a short-chain aliphatic hydrocarbon groupsuch as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl,tert-butyl, pentyl, isopentyl, neopentyl or tert-pentyl group; analicyclic hydrocarbon group such as cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl or cyclohexenyl group; an aromatic hydrocarbongroups such as phenyl, o-tolyl, m-tolyl, p-tolyl, xylyl, mesityl,o-cumenyl, m-cumenyl, p-cumenyl or biphenylyl group; or a combinationthereof As to the aminostyryl groups in R¹⁹ and R²⁰, their amino groupsare in primary, secondary or tertiary amine form and bound to thebenzene rings at their 2- or 4-position against the vinyl groups. Suchamino group may be linked with the benzene ring in the styryl group toform a cyclic structure such as piperidine and julolidine rings.Particular pyran compounds are, for example, those represented byChemical Formulae 28 to 31.

General Formula 6 exemplifies coumarin compounds which are preferable asguest compounds to be used in combination with theluminescence-assisting agent of this invention.

In General Formula 6, R²¹ denotes hydrogen atom or a hydrocarbon groupwhich may bear one or more substituents. Examples of hydrocarbon groupsin R²¹ are aliphatic hydrocarbon groups with a carbon number of up to 5,usually 1 to 4, such as methyl, ethyl, propyl, isopropyl, 1-propenyl,2-propenyl, butyl, isobutyl, sec-butyl, tert-butyl, 2-butenyl and1,3-butadienyl groups; alicyclic hydrocarbon groups such as cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl and cyclohexenyl groups; andaromatic hydrocarbon groups such as phenyl, o-tolyl, m-tolyl, p-tolyl,xylyl, mesityl, o-cumenyl, m-cumenyl, p-cumenyl and diphenylyl groups.One or more hydrogen atoms in such hydrocarbon group may be substitutedby ether groups such as methoxy, trifluoromethoxy, ethoxy, propoxy,isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentyloxy,isopentyloxy, phenoxy and benzyloxy groups; ester groups such asacetoxy, trifluoroacetoxy, benzoyloxy, methoxycarbonyl,trifluoromethoxycarbonyl, ethoxycarbonyl and propoxycarbonyl groups; andhalogen groups such as fluoro, chloro, bromo and iodo groups.

R²² to R²⁵ in General Formula 6 independently denote hydrogen atom or analiphatic hydrocarbon group. Aliphatic hydrocarbon groups in R²² to R²⁵are, for example, those with a carbon number of up to 5, usually 1 to 4,such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl andtert-butyl groups. Dependently upon uses, the much more preferable inorganic EL devices are coumarin compounds where R²² to R²⁵ are aliphatichydrocarbon groups: In particular, those where R²² to R²⁵ are methylgroups are superior in physical and economical properties.

Z in General Formula 6 denotes an aromatic ring which is in condensationwith the thiazole ring. Particular aromatic rings are, for example,monocyclic hydrocarbons such as benzene; condensed polycyclichydrocarbons such as naphthalene, anthracene, phenanthrene, naphthaceneand chrysene; and hydrocarbon ring assemblies such as biphenyl,terphenyl, phenylnaphthalene and naphthylnaphthalene.

Chemical Formulae 32 to 58 exemplify such coumarin compound. Thesecommonly bear a maximum for luminescence such as fluorescence in thevisible region and remarkably prolong a constant luminescence in thegreen to red region over an extended time period when used in organic ELdevices.

Such coumarin compound can be prepared in various ways: With economicalviewpoint, it is preferable to employ the process disclosed in theSpecification of Japanese Patent Application No. 2001-26861 (Title ofthe Invention “Coumarin derivative, process for producing the same, andluminescent agent and luminescent device using the same”); said processincluding the step of allowing a compound which bears aldehyde and ahydrocarbon group at the 3- and 4-positions in coumarin structurerespectively and a julolidine structure at the sites other than the 3-and 4-positions to react with a monocyclic, condensed polycyclic or ringassembly hydrocarbon which bears a thiol group and a primary amino groupbound to vicinal carbon atoms. The coumarin derivatives represented byChemical Formulae 32 to 58 can be obtained in a desired amount with suchprocess. For example, Japanese Patent Kokai No. 2001-76876 illustratescoumarin compounds where R²¹ in General Formula 6 is hydrogen atom.

The reference numeral 5 represents an electron injection/transportationlayer, which is usually formed with a method similar to those in theanode 2 by preparing one or more organic compounds high in electronaffinity or anthraquinodimethane, anthrone, oxaziazole, carbodiimide,distyrylpyrazine, diphenylquinone, silazane, thiopyrandioxide, triazole,tetracarboxylic acid derivative of heterocyclic compound,phthalocyanine, fluorene derivatives, quinolinol metal complexes similarto those in the luminescent layer 4 or a conductive oligomer or polymerof repeating aniline, thiophen or pyrrole units into a membrane with athickness of 10 to 500 nm while allowing it to contact with theluminescent layer 4. In case that a plurality of the electroninjection/transportation layer materials are used, they may be mixed tohomogeneity and then formed into a single layer, and alternativelyformed into a plurality of separate layers without premixing whileallowing each layer to contact with the adjacent layer(s). In case ofproviding a hole-blocking layer, a hole-blocking layer material, forexample, oxadiazole compound such as2-biphenyl-4-yl-5-(4-tert-butylphenyl)-[1,3,4]oxadiazole, 2,2-bis[5-(4-biphenyl)-1,3,4-oxadiazole-2-yl-1,4-phenylene] hexafluoropropaneand 1,3,5-tris-(2-naphthalene-1-yl-[1,3,4]oxadiazole-5-yl)benzen isprepared with a method similar to those in the anode 2 while allowing itto contact with the luminescent layer 4, prior to the formation of theelectron injection/transportation layer 5. The thickness of suchhole-blocking layer is set to a level in the range of 1 to 100 nm,usually, 10 to 50 nm while considering the thickness of the electroninjection/transportation layer 5 and the operation characteristics oforganic EL devices.

The reference numeral 6 represents a cathode, which is usually formed bydepositing one or combined metals such as lithium, magnesium, calcium,sodium, potassium, silver, copper, aluminium, indium, ytterbium, theiralloys and metal oxides and electric conductive compounds with a workfunction (usually not higher than 5 eV) lower than that for the compoundto be used in the electron injection/transportation layer 5 whileallowing the resultant layer to come into contact with the electroninjection/transportation layer 5. There is provided no limitation forthe thickness of the cathode 6: It is set to 10 nm or more thick,desirably, 50-500 nm to give a resistivity of 1 kΩ/□ or lower whileconsidering electric conductivity, production cost, thickness of deviceand optical transmittance. There may be provided an interfacial layer ofaromatic diamine, quinaqcridone, naphthacene, organic silicon or organicphosphide between the cathode 6 and electron injection/transportationlayer 5 in order to improve their adhesion, if necessary. Furthermore,to facilitate the transportation of electrons from the cathode 6 to theinjection/transportation layer 5, there may be provided with a methodsimilar to those in the anode 2 a membrane of alkaline metal or alkalineearth metal compound such as lithium fluoride or lithium oxide, 0.1 to 2nm thick, on the side of contacting to the electroninjection/transportation layer 5 in the cathode 6.

As explained heretofore, the organic EL device of this invention can beobtained by providing in one device an anode, luminescent layer, cathodeand arbitrarily a hole injection/transportation layer, electroninjection/transportation layer and/or hole-blocking layer on the samesubstrate while allowing each layer to contact with adjacent layer(s).During the formation of each layer, it is desirable to carry out all theworking steps under highly vacuumed conditions, particularly, at apressure of 10⁻⁵ Torr or lower to minimize the oxidation anddecomposition of organic compounds, as well as to minimize the adhesionof oxygen and water. In the formation of a luminescent layer, the ratioof host and guest compounds can be adjusted by premixing them in aprescribed ratio, and alternatively by separately controlling theheating velocities for respective compounds in vacuum sublimation. Tominimize deterioration under operation conditions, it is desirableeither to seal a part or whole of the organic EL device thus obtainedwith a sealing glass or metallic cap in the stream of an inert gas, orto coat or cover it with a moisture-proof paint or protecting membranesuch as those of ultraviolet-setting resins. Dependently upon thestructures of organic EL devices, in order to allow the luminescentlayer to release a luminescence outside the device in an improvedefficiency, one can employ one or combined diffracting means whichchange the incident angle of the luminescence against theluminescence-releasing plane in the device, for example, bracelet platesand reflection or transmission gratings of one- or two-dimensional typeto suppress the total reflection at the interface between the organicand inorganic layers in the devices and/or the luminescence-releasingplane and the air.

Now, explanation is made on the way of using the organic EL device ofthis invention. The organic EL device is driven by intermittentlyenergizing it with a relatively high pulse voltage, or continuouslyenergizing it with a relatively low non-pulse voltage, usually, 2 to 50V, dependently upon its uses. The organic EL device of this inventiongives a luminescence only when anode potential exceeds cathodepotential. Thus, both dc or ac voltages are feasible to energize theorganic EL devices of this invention, and the waveform and frequency ofsuch voltages are arbitrary chosen. When energized with ac, the organicEL device of this invention increases and decreases the brightness ofluminescence, and repeats on/off for luminescence due to its principle.In case of the organic EL device in FIG. 1, when a voltage is energizedbetween the anode 2 and cathode 6, holes injected from the anode 2 moveinto the luminescent layer 4 through the electroninjection/transformation layer 3, and electrons injected from thecathode 6 move into the luminescence layer 4 through the electroninjection/transportation layer 5. As the result, the holes and electronsrecouple in the luminescent layer 4, and the prescribed luminescence isreleased from guest compound molecules in the excited state through theanode 2 and substrate 1. Dependently upon the structures and ratio ofhost and guest compounds to be used in combination with the coumarinderivative, the organic EL device of this invention has a maximum forluminescence such as fluorescence in the visible region at a wavelengthlonger than 550 nm, usually, in the orange to red region at a wavelengthof 580 to 780 nm. The x value for such luminescence is usually in therange of 0.30 to 0.73, and the y value, in the range of 0.10 to 0.60 onthe xy chromaticity diagram established by the Commission Internationalde I'Eclairage (CIE).

The organic EL device of this invention would find a variety of uses inilluminants and information displaying equipments to visualizeinformations because it is superior in durability, high in emissionefficiency and as the result easy to elevate its brightness.Particularly, since the illuminants using the organic EL device of thisinvention as light source can be formed into a light panel with areduced power consumption, they are very useful in illuminants ingeneral, as well as energy- and space-saving lighting source orinformation displaying device, for example, those in liquid crystaldevices, copying apparatuses, printing apparatuses, electronicphotographic apparatuses, computers and application apparatuses,controlling instruments directed to industrial uses, electronicmeasuring apparatuses, analyzing apparatuses, measuring instruments ingeneral, communicating apparatuses, electronic measuring instrumentsdirected to uses in medical treatment, electronic equipments in generalwhich are directed to uses at home or professional uses, cars,automobiles, ships, airplanes, spaceships, aircraft controllingapparatuses, interiors, signboards and signs. In case that the organicEL device in this invention is used as displaying means in informationdisplaying equipments such as measuring instruments to be equipped tocars, automobiles, ships, aircrafts and spaceships, computers,televisions, video recorders, computerized game consoles, clocks,calculators, telephones, telecommunicating apparatuses, car navigationsystems, osilloscopes, radars, sonars, signs and signboards, it may bedriven by applying thereto with a driving circuit of conventional simpleor active matrix type which is usual in this art while combining withother organic EL devices which release a visible luminescnce in theblue, green or red region, and/or appropriate filters which are tocontrol luminescent chromaticity and color tone, if necessary.

Several embodiments according to this invention will be explained withreference to Examples:

EXAMPLE 1

Luminescence-Assisting Agent for use in Organic EL Device

An adequate amount of dimethylsulfoxide was placed in a reaction vesseland mixed with 0.21 g of the compound represented by Chemical Formula 59and 0.21 g of the compound represented by Chemical Formula 60. Themixture was refluxed for two hours, cooled to ambient temperature andadmixed with an adequate amount of methanol, followed by collecting theresultant crystals by filtration. The crystals were purified on columnchromatography using a mixture of chloroform and ethyl acetate as eluentto obtain the coumarin derivative of this invention represented byChemical Formula 18 in 0.2 g orange crystals.

A part of the crystals was sampled, and analyzed in usual manner,revealing that the coumarin derivative in this Example showed a meltingpoint of 345 to 351° C. The visible absorption and fluorescence emissionspectra in methylene chloride solution showed an absorptionmaximum(ε=5.8×10⁴) and a fluorescent maximum at wavelengths of 491 and518 nm respectively when determined in usual manner. The ¹H-nuclearmagnetic resonance spectrum (abbreviated as “¹H-NMR spectrum”hereinafter) in chloroform deuteride solution showed peaks at chemicalshifts δ (ppm, TMS) of 1.37 (6H,s), 1.56 (9H, s), 1.62 (6H, s), 1.79(2H,s), 1.85(2H, s), 3.30 (2H, t), 3.39 (2H, s), 7.40 (1H, s), 7.67 (1H,dd), 7.73 (1H, d), 7.90 (1H, d), 7.91 (1H, d), 8.91 (1H, s) and 9.02(1H, s) when determined in usual manner.

Another part of the crystals was sampled and subjected to usual DSCanalysis using a commercially available DSC analyzing system, Trade nameof “Model DSC 220U”, a product of Seiko Instruments Incorporated.,leading to a glass transition point at 151° C. Simultaneously, theconventional analogous compound represented by Chemical Formula 34 wherethe naphtothiazole ring beared no hydrocarbon group was determined forits glass transition point (129° C.) similarly as above. Although theanalogous compound represented by Chemical Formula 61 was significantlylower in solubility in organic solvents such as acetone and chloroformin comparison with the coumarin derivative represented by ChemicalFormula 18 according to this invention, the analogous compound exhibiteda luminescent maximum in a wavelength region similar to that in thecoumarin derivative represented by Chemical Formula 18.

As well known, glass transition point is one of the important merkmalswhich are to estimate the thermal stability of organic compounds: It hasbeen documented that a compound with a higher glass transition pointmarks a larger thermal stability. The above experimental results showthat the coumarin derivative of this invention, which has a condensednaphthalene ring linked with one or more hydrocarbon groups in themolecule, remarkably improves the thermal resistance of conventionalanalogous compounds without substantially changing their desirableoptical properties.

The coumarin derivative of this Example is useful asluminescence-assisting agent because it exhibits an improved thermalresistance and accelerates the transfer of energy from host compound toguest compound.

EXAMPLE 2

Luminescence-Assisting Agent for use in Organic EL Device

The compound represented by Chemical Formula 62 in place of the compoundrepresented by Chemical Formula 59 was allowed to react in accordancewith the method in Example 1 to obtain the coumarin derivativerepresented by Chemical Formula 24 according to this invention.

The coumarin derivative of this Example is useful asluminescence-assisting agent because it exhibits an improved thermalresistance and accelerates the transfer of energy from host compound toguest compound.

EXAMPLE 3

Luminescence-Assisting Agent for use in Organic EL Device

The compounds represented by Chemical Formulae 63 and 64 in place ofthose represented by Chemical Formulae 59 and 60 respectively wereallowed to react in accordance with the method in Example 1 to obtainthe coumarin derivative of this Example represented by Chemical Formula12.

The above coumarin derivative of this Example is useful asluminescence-assisting agent because it exhibits an improved thermalresistance and accelerates the transfer of energy from host compounds toguest compounds.

EXAMPLE 4

Luminescence-Assisting Agent for use in Organic EL Device

The compounds represented by Chemical Formulae 65 and 64 in place ofthose represented by Chemical Formulae 59 and 60 respectively wereallowed to react in accordance with the method of Example 1 to obtainthe coumarin derivative represented by Chemical Formula 11 according tothis invention.

The coumarin derivative of this Example is useful asluminescence-assisting agent because it exhibits an improved thermalresistance and accelerates the transfer of energy from host compound toguest compound.

EXAMPLE 5

Luminescence-Assisting Agent for use in Organic EL Device

The compounds represented by Chemical Formulae 66 and 67 in place ofthose represented by Chemical Formulae 59 and 60 respectively wereallowed to react in accordance with the method in Example 1 to obtainthe coumarin derivative represented by Chemical Formula 2 according tothis invention.

The coumarin derivative of this Example is useful asluminescence-assisting agent because it exhibits an improved thermalresistance and accelerates the transfer of energy from host compound toguest compound.

EXAMPLE 6

Luminescence-Assisting Agent for use in Organic EL Device

A 50 ml aliquot of N,N-dimethylformamide was placed in a reaction vesseland mixed with 13.4 g of the compound represented by Chemical Formula 68and 11.0 g of the compound represented by Chemical Formula 59. Themixture was refluxed for two hours, cooled to ambient temperature andadmixed with an adequate amount of methanol, followed by collecting theresultant crystals by filtration. The crystals were purified on columnchromatography using chloroform as eluent to obtain the coumarinderivative represented by Chemical Formula 20 according to thisinvention.

A part of the crystals was sampled and analyzed in usual manner,revealing that the coumarin derivative in this Example showed a meltingpoint of 251 to 254° C. DSC analysis carried out in Example 1 led aglass transition point at 131° C. The visible absorption andfluorescence emission spectra in methylene chloride solution showed anabsorption maximum(ε=4.2×10⁴) and a fluorescent maximum at respectivewavelengths of 453 and 519 nm when determined in usual manner. The¹H-NMR spectrum in chloroform deuteride solution showed peaks atchemical shifts δ (ppm, TMS ) of 1.37 (6H,s), 1.50 (9H, s), 1.57 (6H,s), 1.78 to 1.87 (4H,m), 3.11 (4H, m), 3.25 to 3.29 (2H, m), 3.34 to3.38 (2H, m), 7.57 (1H, s), 7.66 (1H, dd), 7.75 (1H, d), 7.89 to 7.94(2H, m) and 8.84 (1H, s) when determined in usual manner.

The coumarin derivative of this Example is useful asluminescence-assisting agent because it exhibits an improved thermalresistance and accelerates the transfer of energy from host compound toguest compound.

EXAMPLE 7

Luminescence-Assisting Agent for use in Organic EL Device

Either of six distinct coumarin derivatives, obtained by the methods inExamples 1 to 6, was placed in a water-cooled sublimation apparatus andthen heated in usual manner while keeping the inner space of theapparatus at a reduced pressure to effect sublimation purification.

The coumarin derivatives in this Example are useful in organic ELdevices which need a highly purified luminescence-assisting agent.

Although the coumarin derivatives feasible in this invention, includingthose represented by Chemical Formulae 1 to 27 but not specificallyillustrated in Examples 1 to 7, are slightly different in startingreaction conditions and yields dependently on their structures, they canbe obtained by the methods in Examples 1 to 7 or in accordancetherewith.

EXAMPLE 8

Organic EL Device

A multi-layered organic EL device with the structure of FIG. 1 wasprepared with the luminescence-assisting agent according to thisinvention: A glass substrate with a transparent ITO electrode, 160 nmthick, was patterned with a hydrobromic acid in usual manner, washedwith organic alkali detergent, refined water, acetone and ethanol in thegiven order under ultrasonical conditions, dried, aerated withultraviolet ozone to remove organic impurities on the surface of ITOelectrode, and transferred to the pretreatment room in a vacuumdepositing apparatus. The pretreatment room was then reduced to an innerpressure of 1×10⁻⁶ Torr, injected with a mixture of argon and oxygengases to give an inner pressure of 1×10⁻² Torr, and subjected to plasmatreatment, thus obtaining a clean substrate 1 with ITO electrode as thecathode 2.

The substrate 1 was transferred to the organic vaporizing room in thevacuum depositing apparatus which had been reduced to an inner pressureof 5×10⁻⁷ Torr, while the surface of ITO electrode as the cathode 2 wasattached with an organic membrane-forming mask, after which the carboncrucible was heated to deposit the copper phthalocyanine represented byChemical Formula 69 and triphenylamine tetramer represented by ChemicalFormula 70 (abbreviated as “TPTE” hereinafter) as the holeinjection/transportation layer materials in this order to giverespective thickness of 10 and 30 nm, thus forming the holeinjection/transportation layer 3. Subsequently, TPTE as host compound,the pyran compound represented by Chemical Formula 28 as guest compoundand either of the coumarin derivatives represented by Chemical Formula18 or 20 as luminescence-assisting agent according to this invention,obtained by the method of Example 1 or 6, were simultaneously depositedin a weight ratio of 100:1:3 to form the luminescent layer 4, thicknessof 20 nm while allowing it to contact with the holeinjection/transportation layer 3, after which Tris(8-quinolinolate)aluminium was deposited to form the electron injection/transportationlayer 5, thickness of 60 nm while allowing it to contact with theluminescent layer 4.

Thereafter, the substrate 1 was transferred to the metal-depositing roomin the vacuum depositing apparatus, deposited with lithium fluoride andaluminium in this order to give respective thicknesses of 0.5 and 150 nmto form the anode 6 while allowing it to contact with the electroninjection/transportation layer 5, after which the resultant was sealedwith a glass plate and ultraviolet-setting resin under nitrogen-aeratingconditions, thus obtaining an organic EL device.

Separately, an additional organic EL device as control for comparisonwas prepared similarly as in the above except that the coumarinderivative represented by Chemical Formula 18 or 20 according to thisinvention was omitted. Three types of organic EL devices thus obtainedwere determined in usual manner for electroluminescent properties andlife expectancy (or a driving time to halve initial brightness). Theresults were as shown in Table 1. TABLE 1 Luminescence- Wavelength ofassisting luminescent Chromaticity agent maximum (nm) A B C D diagram(x, y) Remarks Chemical Formula 18 596 551 5.01 3.28 268 (0.55, 0.42)Present invention Chemical Formula 20 596 574 5.22 3.37 418 (0.53, 0.44)Present invention 596 523 4.75 2.26 141 (0.56, 0.41) ControlNote:The symbols “A”, “B”, “C”, and “D” mean “Luminescent brightness (cd/m²),“Current efficiency (cd/A)”, “Power efficiency (lm/W)”, and “Lifeexpectancy (hour)”, respectively.

As seen from the results in Table 1, the organic EL devices in thisExample and control organic EL device commonly exhibited a luminescentmaximum in the orange region at a wavelength of around 600 nm, as wellas an approximately the same chromaticity: In the organic EL devices inthis Example, the x value in color coordinates on the xy chromaticitydiagram established by the CIE was in the range of 0.53 to 0.55; and they value, in the range of 0.42 to 0.44, while in the control organic ELdevice, the x value was 0.56; and the y value, 0.41. This indicates thatthe coumarin derivatives of this invention used in the luminescent layer4 are not responsible for luminescence.

However, as seen in Table 1, the organic EL devices in this Example gaveat ambient temperature a luminescent brightness of 551 to 574 cd/m², apower and current efficiencies exceeding 3 lm/W and 5 cd/A respectivelywhen driven with a constant current of 11 mA/cm². While the controlorganic EL device was significantly inferior to the organic EL devicesin this Example in luminescent brightness (523 cd/m²) when driven with aconstant current of 11 mA/cm² at ambient temperature, and its power andcurrent efficiencies were significantly lower (2.26 lm/W and 4.75 cd/Arespectively) than those in the organic EL devices in this Example. Asto life expectancy, the organic EL devices in this Example gaveprolonged expectancies (268 to 418 hours) when set the initialbrightness to 2,400 cd/m² and driven at ambient temperature with aconstant current, while the control organic EL device was significantlyshorter in life expectancy (141 hours) than those in this Example whentested similarly as above. In the organic EL devices in this example,the electroluminescence consistently prolonged and non-luminescent partssuch as dark spot were observed throughout the test.

These results show that the luminescent efficiency and life expectancyin organic EL devices can be effectively improved without substantiallychanging desirable luminescent properties of guest compounds by usingthe coumarin derivatives of this invention as luminescence-assistingagent in combination with TPTE, a type of hole injection/transportationlayer material.

EXAMPLE 9

Organic EL Device

An organic EL device was prepared similarly as in Example 8 by using thecoumarin derivative represented by Chemical Formula 18 according to thisinvention as luminescence-assisting agent except that the coumarincompound represented by Chemical Formula 39 was used as guest compoundin place of the coumarin derivative represented by Chemical Formula 28.

Separately, an additional organic EL device as control for comparisonwas prepared without using the coumarin derivative of this invention.Two types of organic EL devices thus obtained were determined in usualmanner for electroluminescent properties and life expectancy. Theresults were as shown in Table 2. TABLE 2 Luminescence- Wavelength ofassisting luminescent Chromaticity agent maximum (nm) A B C D diagram(x, y) Remarks Chemical Formula 18 597 252 2.29 1.28 38.2 (0.40, 0.55)Present invention 598 251 2.29 1.26 28.2 (0.38, 0.54) ControlNote:The symbols “A”, “B”, “C”, and “D” mean “Luminescent brightness (cd/m²),“Current efficiency (cd/A)”, “Power efficiency (lm/W)”, and “Lifeexpectancy (hour)”, respectively.

As seen from the results in Table 2, the organic EL device in thisExample and control organic EL device commonly exhibited a luminescentmaximum in the orange region at a wavelength of around 600 nm, as wellas an approximately the same chromaticity: In the organic EL device inthis example, the x value in color coordinates on the xy chromaticitydiagram established by the CIE was 0.40; and the y value, 0.55, while inthe control organic EL device, the x value was 0.38; and the y value,0.54. This indicates that the coumarin derivative of this invention usedin the luminescent layer 4 is not responsible for luminescence.

However, as seen in Table 2, the organic EL device in this Example gaveat ambient temperature a luminescent brightness, power and currentefficiencies similar to those in the control when driven with a constantcurrent of 11 mA/cm²: The organic EL device in this example wassignificantly longer in life expectancy (38.2 hours) than that (28.2hours) in the control when set the initial brightness to 2,400 cd/m² anddriven with a constant current. In the organic EL device in thisExample, the electroluminescence consistently prolonged andnon-luminescent parts such as dark spot were observed throughout thetest.

These results show that the luminescent efficiency and life expectancyin organic EL devices can be effectively improved without substantiallychanging desirable luminescent properties of guest compounds by usingthe coumarin derivative of this invention as luminescence-assistingagent in combination with guest compound such as TPTE.

EXAMPLE 10

Organic EL Device

Organic EL devices were prepared similarly as in Example 8 except thataluminium tris(8-quinolinolate) as host compound and the coumarincompound represented by Chemical Formula 39 as guest compound were usedin place of TPTE and the compound represented by Chemical Formula 28respectively.

Separately, an additional organic EL device as control for comparisonwas prepared without using the coumarin derivative of this invention.Three types of organic EL devices thus obtained were determined in usualmanner for electroluminescent properties and life expectancy. Theresults were as shown in Table 3. TABLE 3 Luminescence- Wavelength ofassisting luminescent Chromaticity agent maximum (nm) A B C D diagram(x, y) Remarks Chemical Formula 18 612 338 3.07 1.84 13 (0.53, 0.45)Present invention Chemical Formula 20 612 373 3.39 1.75 14 (0.50, 0.47)Present invention 614 274 2.49 1.30  8 (0.52, 0.45) ControlNote:The symbols “A”, “B”, “C”, and “D” mean “Luminescent brightness (cd/m²),“Current efficiency (cd/A)”, “Power efficiency (lm/W)”, and “Lifeexpectancy (hour)”, respectively.

As seen from the results in Table 3, the organic EL devices in thisExample and control organic EL device commonly exhibited a luminescentmaximum in the orange region at a wavelength of around 610 nm, as wellas an approximately the same chromaticity: In the organic EL devices inthis example, the x value in color coordinates on the xy chromaticitydiagram established by the CIE was in the range of 0.50 to 0.53; and they value, in the range of 0.45 to 0.47, while in the control organic ELdevice, the x value was 0.52; and the y value, 0.45. This indicates thatthe coumarin derivative of this invention used in the luminescent layer4 are not responsible for the luminescence.

However, as seen in Table 3, the organic EL devices in this Example gaveat ambient temperature a luminescent brightness of 338 to 373 cd/m², apower and current efficiencies exceeding 1.7 lm/W and 3 cd/Arespectively when driven with a constant current of 11 mA/cm². While thecontrol organic EL device was significantly inferior to the organic ELdevices in this Example in luminescent brightness (274 cd/m²) whendriven under the same conditions as above, and its power and currentefficiencies were significantly lower (1.31 m/W and 2.49 cd/Arespectively) than those in the organic EL devices. As to lifeexpectancy, the organic EL devices in this Example gave prolongedexpectancies (13 to 14 hours) when set the initiation brightness to2,400 cd/m² and driven at ambient temperature with a constant current,while the control organic EL device was significantly shorter in lifeexpectancy (8 hours) than those in this Example when tested similarly asabove.

These results show that the luminescent efficiency and life expectancyin organic EL devices can be effectively improved without substantiallychanging desirable luminescent properties of guest compounds by usingthe coumarin derivatives of this invention as luminescence-assistingagent in organic EL devices in combination with quinolinol metalcomplexes, a type of electron injection/transportation layer material.The results of Example 8 to 10 indicate that practically useful organicEL devices can be prepared by using the luminescence-assisting agent ofthis invention in combination with such host and guest compounds,regardless of their carrier transportation properties.

EXAMPLE 11

Organic EL Device

An clean substrate 1 which had been prepared similarly as in Example 8was transferred to the organic vaporizing room in the vacuum depositingapparatus which had been reduced to an inner pressure of 5×10⁻⁷ Torr,while the surface of ITO electrode as the cathode 2 was attached with anorganic membrane-forming mask, after which the carbon crucible washeated, thus forming the hole injection/transportation layer 3.Subsequently, the first luminescent layer comprising TPTE as hostcompound, the pyran compound represented by Chemical Formula 28 as guestcompound and the coumarin derivative as luminescence-assisting agentrepresented by Chemical Formula 18 according to this invention wasformed similarly as in Example 8, after which the compounds representedby Chemical Formulae 71 and 72 were deposited to form the secondluminescent layer, and aluminium tris (8-quinolinolate) was thendeposited to form the third luminescent layer with electroninjection/transportation properties.

Thereafter, the substrate 1 was transferred to the metal-depositing roomin the vacuum depositing apparatus, deposited with lithium fluoride andaluminium in this order similarly as in Example 8 to form the anode 6,after which the resultant was sealed with a glass plate andultraviolet-setting resin under nitrogen-aerating conditions, thusobtaining an organic EL device.

Separately, an additional organic EL device as control for comparisonwas prepared similarly as in the above except that the coumarinderivatives according to this invention was omitted. Two types oforganic EL devices thus obtained were determined in usual manner forelectroluminescent properties and life expectancy. The results were asshown in Table 4. TABLE 4 Luminescence- Wavelength of assistingluminescent Chromaticity agent maximum (nm) A B C D diagram (x, y)Remarks Chemical Formula 18 470, 515, 595 1,198 7.4 3.4 11,000 (0.33,0.36) Present invention 472, 515, 591 1,001 6.8 3.1  6,000 (0.27, 0.41)ControlNote:The symbols “A”, “B”, “C”, and “D” mean “Luminescent brightness (cd/m²),“Current efficiency (cd/A)”, “Power efficiency (lm/W)”, and “Lifeexpectancy (hour)”, respectively.

As seen from the results in Table 4, the organic EL device in thisExample and control organic EL device commonly exhibited respectiveluminescent maxima in the blue, green and orange regions at wavelengthsof 470, 515 and 600 nm respectively which were mixed to give a visiblelight emission in the white region. The organic EL device in thisExample was superior in chromaticity to those of the control: In theorganic EL device in this Example, the x value in color coordinates onthe xy chromaticity diagram established by the CIE was 0.33; and the yvalue, 0.36, while in the control organic EL device, the x value was0.27; and the y value, 0.41.

As seen in Table 4, the organic EL device in this Example gave atambient temperature a luminescent brightness of 1,198 cd/m², a power andcurrent efficiencies of 3.4 lm/W and 7.4 cd/A respectively when drivenwith a constant current of 11 mA/cm². While luminescent brightness andpower and current efficiency in the control organic EL device wereslightly lower (1,001 cd/m², 3.1 lm/W and 6.8 cd/A respectively) thanthat in the organic EL device in this Example. As to life expectancy,the organic EL device in this Example gave a prolonged expectancy(11,000 hours) when set the initial brightness to 300 cd/m² and drivenat ambient temperature with a constant current, while the controlorganic EL device was significantly shorter in life expectancy (6,000hours) than that in this Example when tested similarly as above.

These results show that the luminescent efficiency and life expectancyin organic EL devices can be effectively improved without substantiallychanging desirable luminescent properties of guest compounds by usingthe coumarin derivatives of this invention as luminescence-assistingagent in organic EL devices.

EXAMPLE 12

Display Panel

FIG. 2 is a brief figure of a single matrix type display panel (20stripes of electrodes in the horizontal direction and 30 stripes ofelectrodes in the vertical direction) which comprises the organic ELdevice of this invention as substantial element: Such display panel canbe prepared as follows.

The anode 14 of transparent ITO electrode is formed on one side of theglass substrate 10 in accordance with the method in Example 8, and thenstriped by the wet-etching method. The hole injection/transportationlayer 16 and luminescent layer 18 are formed in this order in accordancewith the method in Example 8, and the cathode 20 is striped with amechanical mask, followed by sealing the organic EL device with a glassplate (not given in the Figure) and ultraviolet-setting resin. In thedisplay panel of this Example, heat radiating means such asheat-radiating plate and cooling fan may be provided on the backside ofthe cathode 20.

EXAMPLE 13

Information Displaying Equipment

FIG. 3 is a block diagram of an information displaying equipment whichuses a display panel prepared by the method in Example 12. In FIG. 3,the reference numeral 30 represents a dc source, output voltage of 4.5V, and its output terminals are connected with a pair ofvoltage-elevating circuits 32 and 34. The voltage-elevating circuit 32is to supply a dc voltage of 5 to 12 V, and its output terminals areconnected with the driving circuit 36. The other voltage-elevatingcircuit 34 is to supply a constant voltage of 5 V to the microcomputer38.

The microcomputer 38 comprises the I/O interface 38 a for exchangingsignals with external sites, the ROM 38 b for recording computerprograms, the RAM 38 c for recording data, and the CPU 38 d for carryingout a variety of operations. To the microcomputer 38 is connected theclock pulse-generating circuit 40 for supplying 8 MHz clock signal andthe oscillating circuits 42 and 44 which are to supply 5 to 50 Hz signalto control the displaying speed and 0.2 to 2 kHz signal to control thescanning frequency respectively.

The reference numeral 48 represents a display panel comprising theorganic EL device of this invention as substantial element, which isconnected with the microcomputer 38 through the driving circuits 36 and46. The driving circuit 36 is to regulate the energization of dc voltagefrom the voltage-elevating circuit 32 to the display panel 48, whichcomprises a plurality of transistors connected with either stripe ofelectrode in the vertical direction in the display panel 48. Thus, wheneither transistor in the driving circuit 36 is turned on, the stripes ofelectrode in the vertical direction connected with the transistor isenergized with the voltage from the voltage-elevating circuit 32. Whilethe driving circuit 46 comprises a plurality of transistors connectedwith either stripe of electrode in the horizontal direction in thedisplay panel 48, and when either transistor in the driving circuit 46is turned on, the stripe of electrode in the horizontal directionconnected with the transistor is grounded.

Since the information displaying equipment in this Example is assembledin this way, when one transistor in the driving circuits 36 and anothertransistor in the driving circuit 46 are turned on in accordance withthe instruction of the microcomputer 38, a prescribed voltage isenergized between corresponding stripes of electrodes in both verticaland horizontal directions in the display panel 48 to allow the organicEL device at the intersection to release a luminescence. Because ofthis, for example, when one stripe of electrode in the horizontaldirection is chosen by appropriately controlling the driving circuit 36,the transistors connected with respective stripes of electrode in thevertical direction are sequentially turned on while grounding the formerstripe of electrode: Thus, the chosen stripe of electrode in thehorizontal direction is wholly scanned to display a prescribed pictureelement. A whole picture can be displayed by sequentially repeating suchscanning in the vertical direction. Since the driving circuit 36 in thisExample has a resistor which can supply a data enough to operate onestripe of electrode, it is desirable to drive transistors with the datarecorded therein.

The information to be displayed is externally supplied in accordancewith displaying rate and frequency, and alternatively supplied with datafrom the ROM 38 b where informations with prescribed patterns such asthose in words has been recorded in the ROM38 b. In case of displayingtelevision broadcast in the usual NTSC mode, the received signals areseparated into horizontal and vertical synchronizing signals incorrespondence with the horizontal and vertical frequencies according tothe broadcasting standard, and the image signals are converted intodigital signals which meet to the pixel number in the display panel 48.Television broadcasts can be displayed on the display panel 48 bysupplying these signals to the microcomputer 38 while appropriatelysynchronizing the signals.

Industrial Applicability

As explained heretofore, this invention is based on the creation of anovel coumarin derivative, as well as on the discovery of its propertiesuseful in industries. The coumarin derivative according to thisinvention effectively accelerates in organic EL devices the transfer ofexcited energy in host compound to guest compound, and as the resultrealizes an organic EL device which is superior in a color purity,luminescent efficiency and life expectancy when used in combination withappropriate host and guest compounds. The organic EL device of thisinvention is advantageously usable in illuminants in general and also ina variety of information displaying equipments to visualizeinformations, for example, those in images and words because it issuperior in luminescent efficiency and durability.

This invention with such outstanding effects is a significant inventionwhich would greatly contributes to this art.

1. An organic electroluminescent device which uses the coumarinderivative represented by either General Formula 1 or 2 as aluminescence-assisting agent:

(In General Formulae 1 and 2, X denotes carbon atom or a heteroatom. R¹to R¹⁴ independently denote hydrogen atom or an arbitrary substituent,provided that R³ and/or R⁴ are apparently absent when R¹ and/or R² forma ring structure containing both the nitrogen atom linked with R¹ and/orR² and the carbon atom linked with R³ or R⁴. At least one of R⁹ to R¹⁴is a hydrocarbon group which may bear a substituent. In case that X is adivalent or trivalent heteroatom, R⁷ and/or R⁸ are absent.)
 2. Theorganic electroluminescent device of claim 1, wherein said coumarinderivative is represented by either General Formula 3 or 4:

(In General Formulae 3 and 4, X denotes carbon atom or a heteroatomsimilarly as in General Formula 1 or
 2. R⁵ to R¹⁴ independently denotehydrogen atom or an arbitrary substituent similarly as in GeneralFormula 1 or
 2. At least one of R⁹ to R¹⁴ is a hydrocarbon group whichmay bear a substituent. In case that X is a divalent or trivalentheteroatom, R⁷ and/or R⁸ are absent. R¹⁵ to R¹⁸ independently denotehydrogen or an arbitrary substituent.)
 3. The organic electroluminescentdevice of claim 1 or 2, which uses as a guest compound thedicyanomethylenepyran or dicyanomethylenethiopyran compound representedby General Formula 5, or the coumarin compound represented by GeneralFormula 6:

(In General Formula 5, Y denotes oxygen or sulfur atoms. R¹⁹ denotes anaminostyryl group, while R²⁰ denotes either another aminostyryl group ora hydrocarbon group. An amino group of said aminostyryl group in R¹⁹and/or R²⁰ may be linked with a benzene ring in a styryl group to form acyclic structures):

(In General Formula 6, R²¹ denotes hydrogen atom or a hydrocarbon groupwhich may bear one or more substituents. R²² to R²⁵ independently denotehydrogen atom or an aliphatic hydrocarbon group, and Z denotes anaromatic ring condensed with a thiazole ring.)
 4. A display panelcomprising the organic electroluminescent device of any one of claims 1to
 3. 5. An information displaying equipment which uses the organicelectroluminescent device of any one of claims 1 to
 3. 6. Aluminescence-assisting agent in organic electroluminescent device whichuses the coumarin derivative represented by either General Formula 1 or2:

(In General Formulae 1 and 2, X denotes carbon atom or a heteroatom. R¹to R¹⁴ independently denote hydrogen atom or an arbitrary substituent,provided that R³ and/or R⁴ are apparently absent when R¹ and/or R² forma ring structure containing both the nitrogen atom linked with R¹ and/orR² and the carbon atom linked with R³ or R⁴. At least one of R⁹ to R¹⁴is a hydrocarbon group which may bear a substituent. In case that X is adivalent or trivalent heteroatom, R⁷ and/or R⁸ are absent.)
 7. Theluminescence-assisting agent of claim 6, wherein said coumarinderivative is represented by either General Formula 3 or 4:

(In General Formulae 3 and 4, X denotes carbon atom or a heteroatomsimilarly as in General Formula 1 or
 2. R⁵ to R¹⁴ independently denotehydrogen atom or an arbitrary substituent similarly as in GeneralFormula 1 or
 2. At least one of R⁹ to R¹⁴ is a hydrocarbon group whichmay bear a substituent. In case that X is a divalent or trivalentheteroatom, R⁷ and/or R⁸ are absent. R¹⁵ to R¹⁸ independently denotehydrogen or an arbitrary substituent.)